1. Field of the Invention
The present invention relates to an intake gasket to be inserted between a cylinder head and a manifold so as to inhibit a temperature increase in an intake manifold.
2. Background Art
A gasket for the manifold of the intake air converging section (intake manifold) in conventional engines is a laminated body of metal plates having a bead formed around the periphery of intake holes (such a gasket being herein referred to as “intake gasket”). The intake gasket is placed between a cylinder head and a manifold. Heat of the cylinder head is transmitted to the manifold via the gasket, thereby increasing the temperature of the manifold. As a result, the temperature of the manifold increases close to the temperature of the cylinder head.
The intake-air temperature must be reduced for increasing the engine output. Because the intake air is sent to the cylinder head via the manifold, the temperature of the manifold itself must be reduced to decrease the temperature of the intake air.
JP-A-06-300139 discloses an intake-exhaust gasket installed on a flange of a cylinder head having counter flow-type intake holes and exhaust holes aligned in the same direction, wherein the intake side is provided with a thin metal plate with an elastic layer coated thereon on both sides of an intermediate plate (claim 1, FIG. 2). This intake-exhaust gasket is effective for both the intake holes and the exhaust holes at the same time, exhibits superior sealing performance, and can be easily installed.
The intake-exhaust gasket described in JP-A-6-300139 has an elastic layer formed of a fiber-reinforced synthetic rubber or synthetic resin of which the coefficient of thermal conductivity is smaller than that of the laminated layer of metal plates. The thickness of the elastic layer, however, is in a range of 50-300 μm, which is insufficient for decreasing the temperature of the manifold itself.
An object of the present invention is, therefore, to provide an intake gasket that can shut out heat from the cylinder head so as to make transmission of heat to the manifold difficult.
In view of the prior art, the inventors of the present invention have conducted extensive studies. As a result, the inventors have found that in an intake gasket comprising an intermediate rib member with a three-layer structure formed from a thin metal plate and rubber layers provided on both sides of the thin metal plate, metal plates disposed on both sides of the intermediate rib member, and elastic metal substrates disposed on both sides of the metal plates, in which the intermediate rib member comprises a first rib formed around the periphery thereof and a second rib around the periphery of a fluid passage hole, if a space is formed from the rib of the intermediate rib member and the metal plates disposed on both sides of the intermediate rib member, the air layer in that space can shut out heat from the cylinder head so as to make transmission of heat to the manifold difficult. This finding has led to the completion of the present invention.